A freestanding bookcase set on carpeting often wobbles and can even tip over. The problem usually occurs because carpet is held in place by tack strips placed along the perimeter of the room. When you set your bookcase (or any other furniture) over the strips, it won’t sit level.
You have a couple of options. The first is to pull the carpet free of the tack strip, cut out a strip of padding where the front corners of the bookcase will sit, and replace the padding with a strip of wood that’s the same thickness as the tack strip, usually 1/4 to 3/8 in. (Option 1).
A second option is to install adjustable feet (called gliders; at home centers) on the corners of the bookcase (Option 2). They’re simple to install—just drill a hole and insert the feet. You won’t have to mess with the carpet, but the feet may be noticeable, which you might not like.
Resist the temptation to simply remove the tack strip. The carpet can move, even under the weight of the bookcase, eventually resulting in a carpet wrinkle in the room.
Regardless of the option you choose, we recommend securing the bookcase to the wall so it can’t tip over. A child climbing or pulling on an unsecured bookcase could knock it over (hundreds of kids are injured each year by falling furniture). Fasten a furniture strap to the wall and the bookcase to keep it from tipping over. The straps cost about $6 at Target and hardware stores. Or, fasten the bookcase to the wall by driving 3-in. screws through the back of the bookcase (at obscure locations) into studs (be sure you hit studs). A total of four screws—two screws into two studs—is plenty.